Flexible insulated air duct is normally made in lengths of twenty-five feet, without end collars, on machines such as that disclosed in U.S. Pat. No. 3,950,213, using core material made by a method such as that disclosed in U.S. Pat. No. 4,299,641. The twenty-five foot lengths are cut at the point of use to other lengths, as required. There is also a demand for shorter lengths with end collars already in place, such as lengths of seven feet and lengths of three and one-half feet, for example. Before my invention, these shorter lengths were made in the factory in an assembly line fashion by cutting up the twenty-five foot lengths and securing end collars on the shorter, cut lengths. The process was labor-intensive and therefore expensive.